Although nouns and verbs provide an adequate classification system for very simple grammatical analyzes, they do not sufficiently account for the fact that sentences are made up of groups of words (and not just subjects and predicates) that function together. Subjects, for example, are not always composed of a single noun; more often than not they are made up of a noun and one or more other words working in conjunction with the noun. For this reason, the discussions that follow use the term phrase regularly. A phrase can be defined as one or more words functioning together as a unit that does not constitute a clause. On this account, the subject and predicate of Dogs bark are made up of a noun phrase (NP) and a verb phrase (VP), respectively, and in The tree was tall, the subject, The tree, also is a noun phrase.
We generally identify a phrase on the basis of a key word at its beginning, such as a noun or a verb. Consider these examples:
• flowers in her hair
• running with the bulls
In the first case, the phrase begins with flowers, which is a noun. In the second case, the phrase begins with running, which is a verb.We also refer to these words as head words because they are at the head of the phrase and the other words in the phrase are attached to them.